Dan Osman risks his life as a matter of course. While on the ground he shuffles simply enough from ad hoc carpentry gigs to loosely defined relationships, dodging cops along the way in a crummy, unregistered pickup. But get him on some obscenely vertical rock, and he becomes a high priest of climbing aesthetes. For two years, Atlantic Monthly columnist Andrew Todhunter followed the Tahoe-area climber and his band of devotees, limning the sublime riches enjoyed by some of the sport's most earnest practitioners. Such riches come at a cost, and a lesser writer could hardly ask us to understand the rationale behind "putting up" challenging new routes that sometimes require months of painstaking work, scaling frozen ice floes in the dark of night, and leaping hundreds of feet from windy bridge buttresses with merely a rope and harness to arrest the fall. But Todhunter pulls it off. In prose that is as exacting as the rock and as graceful as a fine-tuned route, he miraculously transforms Osman's avocation into a reasonable and even artistic profession. The detailed climbing sequences make for compulsive reading, and the author's evocations of Osman's craft will convince even the most ardent flatlander of the endeavor's inherent sanity. What's more, once off the steep pitches, we glimpse a young man strangely vulnerable: trying to win extra cash from sponsors, cobbling together a nontraditional family life, and struggling to maintain his eminence in a sport in which the e